introduction to engineering surveying (ce … systems-2014.… · introduction to engineering...

INTRODUCTION TO ENGINEERING SURVEYING

(CE 1305)

Sr Dr. Tan Liat Choon

Email: [email protected]

Mobile: 016-4975551

Coordinate Systems

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NATIONAL COORDINATE REFERENCE SYSTEM

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• There are 2 types of coordinate systems:

– Geographic Coordinate Systems

– Projected Coordinate Systems

GEOGRAPHIC COORDINATE SYSTEM

• A reference system using latitude and longitude to define the location of points on the surface of a sphere or spheroid

– decimal degrees (DD) -92.5

– degrees/minutes/seconds (DMS) 92 30’ 00” W

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- Earth is not a sphere- Poles are flattened- Bulges at equator

Earth is a spheroid……or ellipsoid4


• Spheroid approximates the shape of the earth

– Model of the earth

– Essentially when surveyors get together and all agree to be wrong

– Also called an “ellipsoid”

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• A datum defines the position of the spheroid relative to the center of the earth

– Origin and orientation of latitude and longitude lines are determined by the datum

– Hundreds of datum customized for different parts of the world

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• Universal Coordinate System (latitude/longitude)• Latitude/longitude good for locating positions on

surface of a globe• Latitude/longitude is not efficient for measuring

distances and areas!– Latitude and longitude are not uniform units of measure– One degree of longitude at equator = 111.321 km (Clarke

1866 spheroid)– One degree of longitude at 60 latitude = 55.802 km (Clarke

1866 spheroid)

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COMMON DATUMS USED IN U.S.• North American Datum 1927 (NAD27)

– Uses the Clarke 1866 spheroid– Reference point is located at Meades Ranch, Kansas – Based on ground survey inrmation in the 1800’s

• North American Datum 1983 (NAD83)– Uses GRS80 (Geodetic Reference System) spheroid– Ellipsoid model from geocentric perspective– Based on ground surveys and satellite information

• WGS 1984 – Most recently developed datum/ framework for measurements worldwide – Earth centered, or geocentric, perspective– This is the datum used by all GPS satellites

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COMMON DATUMS USED IN MALAYSIA

GDM2000 or Geodetic Datum of Malaysia 2000 and Cassini-Soldner are coordinate systems commonly used in the Peninsular Malaysia States of Johor, Negeri Sembilan, Melaka, Pahang, Selangor, Terengganu, Penang/Seberang Perai, Kedah, Perlis, Perak and Kelantan.

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PROJECTED COORDINATE SYSTEMS

• A map projection is the systematic transformation of locations on the earth (latitude/longitude) to planar coordinates

• The basis for this transformation is the geographic coordinate system (which references a datum)

• Map projections are designed for specific purposes

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PROJECTED COORDINATE SYSTEMS

• Use projection to display 3 dimensional locations on to a surface in 2D

• Uses Cartesian coordinates (rectangular)

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INTRODUCTION TO GLOBAL POSITIONING SYSTEM (GPS)

Satellite-based navigation system

Network of 24 satellites placed into orbit by the U.S. Department of Defense (DoD)

GPS was developed and is operated by the U.S. DoD. Originally called NAVSTAR (Navigation System with Timing and Ranging). Before its civilian applications, GPS was originally intended for military applications to provide all-weather round-the-clock navigation capabilities for military ground, sea, and air forces

1980s, system available for civilian use

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GPS works in any weather conditions, anywhere in the world, 24 hours a day. No subscription fees or setup charges to use GPS

Applications – navigation, location determination

Used for cartography, forestry, mineral exploration, wildlife habitation management, monitoring the movement of people and things and bringing precise timing to the world

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A worldwide MEO satellite navigational system formed by 24 satellites orbiting the earth and their corresponding receivers on the earth

Orbit the earth at approximately 12,000 miles above the surface and make two complete orbits every 24 hours

Continuously transmit digital radio signals that contain data on the satellites location and the exact time to the earth-bound receivers

Equipped with atomic clocks within a billionth of a second precision. Based on this information the receivers know how long it takes for the signal to reach the receiver on earth

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As each signal travels at the speed of light, the longer it takes the receiver to get the signal, the farther away the satellite is. By knowing how far away a satellite is, the receiver knows that it is located somewhere on the surface of an imaginary sphere centred at the satellite

By using three satellites, GPS can calculate the longitude and latitude of the receiver based on where the three spheres intersect

By using four satellites, GPS can also determine altitude 15


MEO, medium or middle earth orbit, a satellite system used in telecommunications

MEO satellites orbit the earth between 1,000 and 22,300 miles above the earth's surface

MEOs are mainly used in geographical positioning systems and are not stationary in relation to the rotation of the earth

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ELEMENTS OF GPS Space Segmento Consists of a constellation of 24 satellites (and about six

"spares"), each in its own orbit 20200 kilometres above Earth. Four additional satellites are held in reserve as spares

Control Segmento Consists of ground stations (6 of them, located around the

world) that make sure the satellites are working properly. The master control station at Schriever Air Force Base, near Colorado Springs, Colorado, runs the system

Users Segmento Consists of receivers, which you can hold in your hand or

mount in a vehicle, like your car, stationary17

ELEMENTS OF GPS

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SPACE SEGMENT (CONSTELLATION OF SATELLITES)

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An orbit is one trip in space around Earth for 24 hours satellite coverage

The satellites travel in near-circular orbits that have a mean altitude of 20,200 km above the earth and orbital period of 12 hours to orbit Earth

Precise atomic clocks are used in the GPS satellites so that it keeps time to within three nanoseconds - that’s 0.000000003, or three-billionths, of a second

Broadcast signals synchronized with those from other satellites

The signal travels at the speed of light. Even at this speed, the signal takes a measurable amount of time to reach the receiver 20


• The difference between the time when the signal is received and the time when it was sent, multiplied by the speed of light, enables the receiver to calculate the distance to the satellite

• For more accurate measurement, the GPS navigation signals are specially designed for GPS receivers to measure the time of arrival and to allow all the satellites to operate on the same frequency without interfering with each other

• To calculate its precise latitude, longitude, and altitude, the receiver measures the distance to four separate GPS satellites. By using four satellites, the receiver calculates both its position and the time and doesn't need an expensive atomic clock like those on the satellites

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MCS Colorado Springs

Hawaii

Buenos Aires

US NIMA Tracking Sites

Diego Garcia

Ascension

Bahrain

Kwajalein

Smithfield

US Airforce Tracking SitesUS Airforce Upload Sites

Hermitage

Ouito

US Air Force and NIMA Control and Tracking Stations

See also map at <http://164.214.2.59/GandG/sathtml>MCS – Master Control Station

CONTROL SEGMENT (GROUND STATION)


The GPS control segment consists of twelve monitoring stations located around the world

A master control station at Schriever Air Force Base in Colorado Springs, Colorado

Six monitor stations: Hawaii and Kwajalein in the Pacific Ocean; Diego Garcia in the Indian Ocean; Ascension Island in the Atlantic Ocean; Cape Canaveral, Florida and Colorado Springs, Colorado

Four large ground-antenna stations send commands and data up to the satellites and collect telemetry back from them

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The monitor stations track the navigation signals and send their data back to the master control station. There, the controllers determine any adjustments or updates to the navigation signals needed to maintain precise navigation and update the satellites via the ground antennas.

To further improve system accuracy, in 2005, the master control station added data from six monitor stations operated by the National Geospatial-Intelligence Agency to the six GPS monitor stations

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USER SEGMENT (RECEIVERS)

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GPS receivers can be carried in your hand

Installed on aircraft, ships, tanks, submarines, cars, and trucks

Stationary

These receivers detect, decode, and process GPS satellite signals

More than 100 different receiver models are already in use 27


The typical hand-held receiver is about the size of a cellular telephone, and the newer models are even smaller and fit in a wristwatch or a Personal Data Assistant

The commercial hand-held units distributed to U.S. armed forces personnel during the Persian Gulf War weighed only 28 ounces (less than two pounds). Since then, basic receiver functions have been miniaturized onto integrated circuits that weigh about one ounce

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SIGNALS GPS satellites transmit two low power radio signals, designated L1 and L2.

Recently L5

Civilian GPS uses the L1 frequency of 1575.42 MHz and L2 frequency of 1227.60 MHz in the UHF band

The signals travel by line of sight, meaning they will pass through clouds, glass and plastic but will not go through most solid objects such as buildings and mountains

A GPS signal contains three different bits of information - a pseudorandom code, ephemeris data and almanac data

The pseudorandom code is simply an I.D. code that identifies which satellite is transmitting information. You can view this number on your GPS unit's satellite page, as it identifies which satellites it's receiving

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SIGNALS

Ephemeris data tells the GPS receiver where each GPS satellite should be at any time throughout the day. Each satellite transmits ephemeris data showing the orbital information for that satellite and for every other satellite in the system

Almanac data, which is constantly transmitted by each satellite, contains important information about the status of the satellite (healthy or unhealthy), current date and time. This part of the signal is essential for determining a position

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SOURCES OF ERROR IN GPSFactors that can degrade the GPS signal and thus affect accuracy include the following:

o Ionosphere and troposphere delays — The satellite signal slows as it passes through the atmosphere. The GPS system uses a built-in model that calculates an average amount of delay to partially correct for this type of error

o Signal multipath — This occurs when the GPS signal is reflected off objects such as tall buildings or large rock surfaces before it reaches the receiver. This increases the travel time of the signal, thereby causing errors

o Receiver clock errors — A receiver's built-in clock is not as accurate as the atomic clocks onboard the GPS satellites. Therefore, it may have very slight timing errors

o Orbital errors — Also known as ephemeris errors, these are inaccuracies of the satellite's reported location

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SOURCES OF ERROR IN GPSo Number of satellites visible — The more satellites a GPS receiver

can "see," the better the accuracy. Buildings, terrain, electronic interference, or sometimes even dense foliage can block signal reception, causing position errors or possibly no position reading at all. GPS units typically will not work indoors, underwater or underground

o Satellite geometry/shading — This refers to the relative position of the satellites at any given time. Ideal satellite geometry exists when the satellites are located at wide angles relative to each other. Poor geometry results when the satellites are located in a line or in a tight grouping

o Intentional degradation of the satellite signal — Selective Availability (SA) is an intentional degradation of the signal once imposed by the U.S. Department of Defense. SA was intended to prevent military adversaries from using the highly accurate GPS signals. The government turned off SA in May 2000, which significantly improved the accuracy of civilian GPS receivers

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HOW DOES GPS WORKS The principle behind GPS is the measurement of distance (or

“range”) between the satellites and the receiver

The satellites tell us exactly where they are in their orbits by broadcasting data the receiver uses to compute their positions

It works something like this: o If we know our exact distance from a satellite in space, we know we are somewhere on

the surface of an imaginary sphere with a radius equal to the distance to the satellite radius

o If we know our exact distance from two satellites, we know that we are located somewhere on the line where the two spheres intersect

o And, if we take a third and a fourth measurement from two more satellites, we can find our location. The GPS receiver processes the satellite range measurements and produces its position 33

HOW DOES GPS WORKS

GPS uses a system of coordinates called WGS 84, which stands for World Geodetic System 1984

It allows surveyors all around the world to produce maps like the ones you see in school, all with a common reference frame for the lines of latitude and longitude that locate places and things

Likewise, GPS uses time from the United States Naval Observatory in Washington, D.C., to synchronize all the timing elements of the GPS system, much like Harrison's chronometer was synchronized to the time at Greenwich

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HOW DOES GPS WORKS

Now you should have a fairly clear picture of the GPS system:

o You know that it consists of satellites whose paths are monitored by ground stations

o Each satellite generates radio signals that allow a receiver to estimate the satellite location and distance between the satellite and the receiver

o The receiver uses the measurements to calculate where on or above Earth the user is located

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USES OF GPSFor Military

o GPS system has already proved to be a valuable aid to U.S. military forces

o With GPS the soldiers were able to go places and manoeuvre in sandstorms or at night. More than 1,000 portable commercial receivers were initially purchased for their use

o The demand was so great that before the end of the conflict, more than 9,000 commercial receivers were in use in the Gulf region. They were carried by soldiers on the ground and were attached to vehicles, helicopters, and aircraft instrument panels

o Navy ships used them for rendezvous, minesweeping, and aircraft operations 36

USES OF GPS

For Civilianso GPS is helping to save lives and property across the nation.

Example:

o In 2002, it enabled rescuers to drill a shaft to free trapped miners in Somerset

o Many police, fire, and emergency medical-service units use GPS receivers to determine the police car, fire truck, or ambulance nearest to an emergency, enabling the quickest possible response in life-or-death situations

o GPS-equipped aircraft can quickly plot the perimeter of a forest fire so fire supervisors can produce updated maps in the field and send fire fighters safely to key hot spots

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USES OF GPS

For Constructions

o Mapping, construction, and surveying companies use GPS extensively

o During construction of the tunnel under the English Channel, British and French crews started digging from opposite ends: one from Dover, England, and one from Calais, France. They relied on GPS receivers outside the tunnel to check their positions along the way and to make sure they met exactly in the middle. Otherwise, the tunnel might have been crooked

Example :

o GPS allows mine operators to navigate mining equipment safely, even when visibility is obscured

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USES OF GPSGPS-equipped fleet vehicles, public transportation

systems, delivery trucks, and courier services use receivers to monitor their locations at all times for both efficiency and driver safety

Automobile manufacturers are offering moving-map displays guided by GPS receivers as an option on new vehicles. The displays can be removed and taken into a home to plan a trip. Several major rental car companies have GPS-equipped vehicles that give directions to drivers on display screens and through synthesized voice instructions 39

USES OF GPS

GPS-equipped balloons monitor holes in the ozone layer over the polar regions as well as air quality across the nation

Buoys tracking major oil spills transmit data using GPS to guide cleanup operations

Archaeologists, biologists, and explorers are using the system to locate ancient ruins, migrating animal herds, and endangered species such as manatees, snow leopards, and giant pandas

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T h a n k Yo u &

Q u e s t i o n A n d A n s w e r

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